Research

Areas of Research in Which Dr. Tour has Made a Contribution

Graphene nanoribbons—I have so far published >39 papers detailing our progress in the synthesis, derivatization and use of graphene nanoribbons (GNRs) in many materials. The first synthesis from multiwalled carbon nanotubes (MWCNTs) using an acidic oxidation produced GNRs with many defects that lowered their conductivity and usefulness for composites. However, the addition of a weaker acid to the oxidation mixture led to the synthesis of GNRs with fewer defects and the process is now licensed to EMD-Merck. We then found that MWCNTs could be split using potassium vapor and later a sodium/potassium alloy in the liquid phase. The splitting in the liquid phase produced intermediate materials with anions along the GNR edges that could be functionalized using alkyl iodides. The alkyl functionalized GNRs were used in radio-frequency-transparent, electrically conductive GNR thin films as deicing heating layers; in polyurethane composite film for improved gas barrier and mechanical performances; and in dispersible ferromagnetic GNR stacks with enhanced electrical percolation properties in a magnetic field, along with other applications. I directed the research that is detailed in the following papers.

a. Kosynkin, D. V.; Higginbotham, A. L.; Sinitskii, A.; Lomeda, J. R.; Dimiev, A.; Price, B. K.; Tour, J. M. Longitudinal Unzipping of Carbon Nanotubes to Form Graphene Nanoribbons. Nature 2009, 458, 872-826.
b. Higginbotham, A. L.; Kosynkin, D. V.; Sinitskii, A.; Sun, Z.; Tour, J. M. Low-Defect Graphene Oxide Nanoribbons from Multiwalled Carbon Nanotubes, ACS Nano 2010, 4, 2059-2069.
c. Kosynkin, D. V.; Lu, W.; Sinitskii, A.; Pera, G.; Sun, Z.; Tour, J. M. Highly Conductive Graphene Nanoribbons by Longitudinal Splitting of Carbon Nanotubes Using Potassium Vapor, ACS Nano 2011, 5, 968-974.
d. Lu, W.; Ruan, G.; Genorio, B.; Zhu, Y.; Novosel, B.; Tour, J. M. Functionalized Graphene Nanoribbons via Anionic Polymerization Initiated by Alkali Metal-Intercalated Carbon Nanotubes. ACS Nano, 2013, 7, 2669–2675.

Silicon oxide memory—we discovered that silicon oxide, thought by some to be only useful as an insulating layer in memory devices, to be additionally useful as an active component. This work was started by an exceptional graduate student, Jun Yao, who was co-advised by Prof. Douglas Natelson, Prof. Lin Zhong and me. Jun gathered much data before he convinced me that what he was seeing was real. The mechanism of the memory process was imaged and transparent nonvolatile resistive memory devices were fabricated using silicon oxide and graphene, and other materials. This technology holds promise for use in wearable electronics and other applications where transparent memory could be important and the process is now being commercialized by Weebit LLC.

a. Yao, J.; Zhong, L.; Natelson, D.; Tour, J. M. Silicon Oxide: A Non-innocent Surface for Molecular Electronics and Nanoelectronics Studies. J. Am. Chem. Soc. 2011, 133, 941-948.
b. Yao, J.; Zhong, L.; Natelson, D.; Tour, J. M. Intrinsic Resistive Switching and Memory Effects in Silicon Oxide. Appl. Phys. A 2011, 102, 835-839.
c. Yao, J.; Zhong, L.; Natelson, D.; Tour, J. M. In situ Imaging of the Conducting Filament in a Silicon Oxide Resistive Switch. Nature Scientific Reports 2012, 2:242, 1-5.
d. Yao, J.; Lin, J.; Dai, Y.; Ruan, G.; Yan, Z.; Li, L.; Zhong, L.; Natelson, D.; Tour, J. M. Highly Transparent Nonvolatile Resistive Memory Devices from Silicon Oxide and Graphene. Nature Commun. 2012, 3, 1-8.

Graphene from solid carbon sources—it was known that graphene could be made from physical separation of individual layers by painstakingly pealing graphene away from graphite using adhesive tape. An easier approach was the chemical vapor phase deposition (CVD) of solid graphene from a gaseous carbon source on a metal catalyst such as copper. I discovered that solid carbon sources such as common polymers, organic chemicals and even food, insects and wastes could be used to produce graphene when heated on copper. Additionally, the heating of functionalized carbon nanotubes on a metal catalyst surface produced graphene by decomposition of the functional addends to form a composite that was reinforced by carbon nanotubes (rebar graphene). We recently discovered that porous graphene films could be synthesized by exposing commercially available polyimide to laser radiation. This has led to many follow-on developments that will be published. I led the synthesis research with high resolution imaging by Prof. Miguel Yacaman, from the University of Texas at San Antonio and some collaboration with the late Rice University Senior Faculty Fellow Robert Hauge.

a. Sun, Z.; Yan, Z.; Yao, J.; Beitler, E.; Zhu, Y.; Tour, J. M. Growth of Graphene from Solid Carbon Sources. Nature 2010, 468, 549-552.
b. Ruan, G.; Sun, Z.; Peng, Z.; Tour, J. M. Growth of Graphene from Food, Insects, and Waste. ACS Nano 2011, 5, 7601-7607.
c. Yan, Z.; Peng, Z.; Casillas, G.; Lin, J.; Xiang, C.; Zhou, H.; Yang, Y.; Ruan, G.; Raji, A.-R. O.; Samuel, E. L. G.; Hauge, R. H.; Yacaman, M. J.; Tour, J. M. Rebar Graphene. ACS Nano, 2014, 8, 5061-5068.
d. Lin, J.; Peng, Z.; Liu, Y.; Ruiz-Zepeda, F.; Ye, R.; Samuel, E. L. G.; Yacaman, M. J.; Yakobson, B. I.; Tour, J. M. Laser-Induced Porous Graphene Films from Commercial Polymers. Nature Comm. 2014, 5:5714.

Nanocars and nanomachines—the synthesis of a nanomachine that could roll on a surface had been a goal of mine since I was at the University of South Carolina. It took my lab about 10 years to finalize the synthesis and obtain images of movement via SEM from collaborator Prof. Kevin Kelly. The nanomachines, referred to as “nanocars” in my presentations and publications, drew avid attention from the general public because people could relate the chemical structures to real world objects such as cars and trucks, machines with which everyone is familiar. Our 2005 paper in Nano Letters was the most downloaded article of all American Chemical Society journal articles that year. We continue to investigate the synthesis of nanocars and nanomachines, some with internal motors and moieties that would make them easier to image. I have published at least 15 papers on nanocar synthesis, imaging and movement. I directed all of the synthetic work; my group worked with collaborators for the imaging.

a. Shirai, Y.; Osgood, A. J.; Zhao, Y.; Kelly, K. F.; Tour, J. M. Directional Control in Thermally Driven Single-Molecule Nanocars. Nano Lett. 2005, 5, 2330-2334.
b. García-Lopez, V.; Chiang, P.-T.; Chen, F.; Ruan, G.; Martí, A. A.; Kolomeisky, A. B.; Wang, G.; Tour, J. M. Unimolecular Submersible Nanomachines. Synthesis, Actuation, and Monitoring. Nano Lett. 2015, 15, 8229–8239.
c. García-Lopez, V.; Jeffet, J.; Kuwahara, S.; Martí, A. A.; Ebenstein, Y.; Tour, J. M. Synthesis and Photostability of Unimolecular Submersible Nanomachines: Toward Single-Molecule Tracking in Solution. Org. Lett. 2016, 18, 2343–2346.
d. Chen, F.; García-Lopez, V.; Jin, T.; Neupane, B.; Chu, P.-L. E. Tour, J.; Wang, G. Moving Kinetics of Nanocars with Hydrophobic Wheels on Solid Surfaces at Ambient Conditions. J. Phys. Chem. C 2016, 120, 10887-10894.

Poly(ethylene glycol) functionalized hydrophilic carbon clusters (PEG-HCCs) as antioxidants—I am particularly interested in this area of research since oxidation has been shown to be present in many disease states and injury pathways. Successful implementation of a clinical solution to provide protection against and healing from injurious oxidation pathways could be the answer to curing or alleviating suffering from diabetes, traumatic brain injury, non-alcoholic fatty liver disease and other illnesses. I first discovered the antioxidant capabilities of PEG-HCCs in 2009 and have been pursuing testing in vitro and in vivo with a number of collaborators in the Texas Medical Center hospitals and research centers such as Prof. Robia Pautler, Prof. Christine Beeton and Prof. Thomas Kent, from Baylor College of Medicine; Prof. Ah-Lim Tsai, from the University of Texas Health Science Center Houston; Prof. David Baskin, from the Methodist Hospital Research Institute; and Prof. Jeff Myers, from MD Anderson Cancer Center Houston. We have used the PEG-HCC nanoparticles alone and have also sequestered or covalently attached functionality to the nanoparticles. This has been a fruitful area of research that I want to continue because of its potential impact on many diseases of interest.

a. Bitner, B. R.; Marcano, D. C.; Berlin, J. M.; Fabian, R. H.; Cherian, L.; Culver, J. C.; Dickinson, M. E.; Robertson, C. S.; Pautler, R. G.; Kent, T. A.; Tour , J. M. Antioxidant Carbon Particles Improve Cerebrovascular Dysfunction Following Traumatic Brain Injury. ACS Nano 2012, 6, 8007–8014.
b. Marcano, D. C.; Bitner, B. R.; Berlin, J. M.; Jarjour, J.; Lee, J. M.; Jacob, A.; Fabian, R. H.; Kent, T. A.; Tour , J. M.“Design of Poly(ethylene glycol)-functionalized Hydrophilic Carbon Clusters for Targeted Therapy of Cerebrovascular Dysfunction in Mild Traumatic Brain Injury. J. Neurotrauma, 2013, 30, 789-796.
c. Samuel, E. L. G.; Duong, M. T.; Bitner, B. R.; Marcano, D. C.; Tour, J. M.; Kent, T. A. Hydrophilic Carbon Clusters as Therapeutic, High-Capacity Antioxidants. Trends Biotech. 2014 32, 501-505.
d. Samuel, E. L. G.; Marcano; D. C.; Berka, V.; Bitner, B. R.; Wu, G; Potter, A.; Fabian, R. H.; Pautler, R. G.; Kent, T. A.; Tsai, A.-L.; Tour, J. M. Highly Efficient Conversion of Superoxide to Oxygen Using Hydrophilic Carbon Clusters. Proc. Nat. Acad. Sci. 2015, 112, 2343–2348.

The “All Publications” page is an updated list of publications in all of these areas and more.